The present invention relates to a filtering device and in particular a filtering device in connection with a sampler for a fiber suspension sampler.
In the paper and cellulose industry and its processes there is a need for continuously monitoring the process regarding the wood fibers and their quality and appearance, such as length, curvature, and the like.
Often are devices used, which take samples of a certain defined volume directly from an ongoing process, such as from a process pipe with floating fiber suspension. Many of the types of devices comprise an elongated body, which is moved into the suspension whereby the end of the elongated body is provided with a compartment, into which the suspension sample enters. The elongated body is then withdrawn until the sample compartment is positioned in a chamber of the device. The chamber is connected to an inlet for liquid and an outlet out of which the sample is transported by the incoming liquid. The sample together with the liquid is then fed to an analysing equipment where the suspension is tested. Examples of such devices are disclosed in for example patent documents U.S. Pat. No. 4,147,062 and WO 99/42806.
If the sample contains particles with a rather large size, larger than expected, or the suspension is rather thick, ie a rather high fiber content in the suspension, there is a risk that either the particles will block the outlet so that not all of the sample is fed to the analysing equipment, or that the fibers will either lock the outlet due to the thickness or not all of the sample is dissolved.
One solution is then to have rather large outlet passages so as to avoid blocking of the outlet. One problem is then that larger particles, that usually are not fibers, are fed to the analysing equipment. These may disturb the testing, or worse, damage the equipment. Further, large parts of fibers are also not wanted since they affect the testing, in particular when the appearance of the fibers are to be monitored.
The object of the present invention is to ascertain that the samples taken from a flow of suspension is treated and fed to the analysing device in a manner that the complete sample is available and that the sampling device is not blocked by either larger particles or fiber.
The object is achieved according to one aspect of the invention by a filtering device for preventing passing and blocking of unwanted particles in a suspension, which filtering device comprises an inlet and an outlet and a defined space between the inlet and the outlet, wherein the device comprises a filter means arranged in the outlet, that the filter means is arranged with openings, that the size of the openings permit particles of a size smaller than the openings to pass through, and at least one nozzle connected to a pressurised liquid source, capable of delivering a liquid jet, and arranged adjacent said outlet, wherein the said at least one nozzle is arranged such and directed such that particles that engage said filter means are removed therefrom by the liquid jet.
According to another aspect of the invention, the at least one nozzle is directed such that a swirling effect also is obtained in the defined space by the liquid jet.
According to a further aspect of the invention, the said filter means is the outlet opening, and that the said liquid jet from the said at least one nozzle is directed through the outlet opening and towards the defined space.
In another embodiment of the invention, the said filter means comprises a mesh arranged in said outlet opening, and that the said liquid jet from the said at least one nozzle is directed through the outlet opening and towards the defined space.
According to the invention the said at least one nozzle may be arranged and directed in a plurality of ways in order to prevent blocking of unwanted particles at the filter means.
The filtering device according to the invention may further comprise nozzles that are arranged and directed such in the defined space as to enhance the swirling effect in the defined space.
With the filtering device according to the invention any larger objects are effectively prevented from passing from the sample chamber to the measuring device, thereby preventing any objects from disturbing the measurement or even damaging the measuring equipment. The size of the outlet opening is chosen such that particles above a certain size are effectively prevented from passing. At the same time, the liquid jet from the nozzle prevents the unwanted particles from blocking the outlet opening.
The additional advantage with the liquid jet is that it causes a swirling effect inside the defined space. The swirling effect has the function of diluting the suspension and also in dissolving the suspension, which may be particularly important when dealing with rather thick pulp suspensions. In that context further liquid jet nozzles may be used, which are arranged and directed such that the jet affects the suspension and not necessarily adjacent the outlet opening.
These and other aspects of the present invention and further advantages with it will become apparent from the following detailed description of the invention and from the accompanying drawings.